Magnetic Resonance Imaging of Parotid Oncocytoma

Oncocytomas are a group of rare neoplasms occurring in the parotid gland and account for less than 1% of all salivary gland tumors. Oncocytoma is a benign tumor composed of oncocytes with many hyperplastic mitochondria, usually presenting a solitary nodule. We reported a rare case of a slow-growing parotid oncocytoma in a 73-year-old woman who presented with a palpable mass in the left infra-auricular region for about 7 years. MRI showed a welldefined hypointense mass on T1-weighted images (T1WI) and isoto slightly hypointensity on short inversion time inversion recovery (STIR) images compared to the parotid gland parenchyma. Moderate tumor enhancement was noted after intravenous gadolinium-based contrast medium administration. The patient underwent left parotidectomy and the histopathological examination confirmed the diagnosis of oncocytoma. The characteristic MR imaging features with their differential diagnosis are discussed and literatures reviewed. Correspondence Author to: Jhy-Shyan Gau Department of Radiology, E-DA Hospital/I-Shou University, Kaohsiung, Taiwan No. 1, Yi-Da Road, Yan-Chau, Kaohsiung 824, Taiwan J Radiol Sci 2011; 36: 165-168 MRi of parotid oncocytoma 166 J Radiol Sci September 2011 Vol.36 No.3 1a 1c Figure 1. a. Pre-contrast axial T1-weighted and b. axial STIR images, MRI reveals a mass in the deep lobe of left parotid gland. The mass displays low signal intensity to the parotid gland on T1WI and isoto slightly hypointensity on STIR images. (arrows) c. Post-contrast axial T1-weighted image with fat suppression shows moderate enhancement of the mass. (arrow) 1b Figure 1 MRi of parotid oncocytoma 167 J Radiol Sci September 2011 Vol.36 No.3 cells with small uniform size nuclei in small lobular and acinic patterns. There was no necrosis or mitosis. The final diagnosis of parotid gland oncocytoma was confirmed. After surgery, the patient recovered well without facial nerve weakness or any other complications. During the follow-up period, no obvious recurrent tumor could be found.